1. Field of the Invention
This invention relates generally to a nozzle having a variable throat barrier, and particularly to a converging-diverging nozzle in which a throat area of same is defined an annulus formed by converging streams of ions, and the like.
2. Description of the Prior Art
Although the general objective for most applications of rocket motors, and the like, is to produce a large thrust for a very limited period, the use of rocket motors with space shuttles, and the like, has created a need for variable-thrust rocket engines which can permit the thrust of the engine to be varied as a function of a specific maneuver of the associated vehicle. For efficient performance of a given rocket-motor, for a specific propellant combination and a constant total pressure at the entrance to an associated exhaust nozzle, the thrust developed by the rocket motor is directly proportional to the cross-sectional area of the throat of the exhaust nozzle. In other words, it is desireable to have a rocket engine burning propellants at a constant rate and varying the throat area of the exhaust nozzle in order to vary the engine thrust as desired.
It is known that a stream of ions can be used for propelling spacecrafts in, for example, the vacuum of outerspace. While positively charged ions have comparatively little mass, substantial thrust can be generated by an accelerated stream of such ions. One manner of generating a stream of ions is by the use of a linear particle accelerator which moves the particles, or ions, in a straight line. Although the source of particles for the first accelerators was the simplest of atomic elements, namely hydrogen, Cesium and other liquid metals are also employed as particle sources. Acceleration of the particles is accomplished by subjecting them to an electrical force. More specifically, the charge on the particle being accelerated can be used to accomplish the desired acceleration by use of other polarity electrical charges, or by alternating polarity of electrical charges subjected to the particles.
In linear accelerators, the acceleration is achieved by use of a plurality of electrodes, usually referred to as drift tubes, having increased length as they are arranged along the path of travel of a particle stream, and having alternate polarity electrical charges placed on them according to predetermined timing cycle. Since the frequency of an actuating signal generator is constant, an alternating current generator commonly being employed, each successive tube must be longer so that the ions will travel within each tube for the same length of time, but at a higher speed, as the ions proceed downstream of the series of tubes.